Detecting a tracer in a hydrocarbon reservoir

ABSTRACT

The present disclosure describes methods and systems for detecting a tracer in a hydrocarbon reservoir. One method includes injecting a tracer at a first location in a reservoir, wherein the tracer mixes with subsurface fluid in the reservoir; collecting fluid samples at a second location in the reservoir; mixing a magnetic surface-enhanced Raman scattering (SERS) particle with the fluid samples; applying a magnetic field to the mixed fluid samples; and analyzing the fluid samples to detect a presence of the tracer in the fluid samples.

TECHNICAL FIELD

This disclosure relates to detecting tracers in a hydrocarbon reservoir.

BACKGROUND

In a hydrocarbon reservoir, subsurface fluid flow patterns can beanalyzed to develop a geological model for the hydrocarbon reservoir.The model can be used to generate one or more parameters that are usefulin reservoir resource management, including, for example, well to wellconnectivity, fluid allocation, fracture locations, swept volumes, andresidual oil saturations.

SUMMARY

The present disclosure describes methods and systems for detectingtracers in a hydrocarbon reservoir. One method includes injecting atracer at a first location in a reservoir, wherein the tracer mixes withsubsurface fluid in the reservoir; collecting fluid samples at a secondlocation in the reservoir; mixing a magnetic surface-enhanced Ramanscattering (SERS) particle with the fluid samples; applying a magneticfield to the mixed fluid samples; and analyzing the fluid samples todetect a presence of the tracer in the fluid samples. Otherimplementations include corresponding systems and apparatuses. Otherimplementations of this aspect include corresponding systems andapparatuses configured to perform the actions of the methods.

The details of one or more implementations of the subject matter of thisdisclosure are set forth in the accompanying drawings and the subsequentdescription. Other features, aspects, and advantages of the subjectmatter will become apparent from the description, the drawings, and theclaims.

DESCRIPTION OF DRAWINGS

The patent or application file contains at least one color drawingexecuted in color. Copies of this patent application publication withcolor drawing(s) will be provided by the Patent and Trademark Officeupon request and payment of the necessary fee.

FIG. 1 is a schematic diagram that illustrates an example tracerdetection system, according to an implementation.

FIG. 2 illustrates a tracer detection platform before a magnetic fieldis applied and a tracer detection platform after the magnetic field isapplied, according to an implementation.

FIG. 3 is a schematic diagram that illustrates an example process forproducing the SERS-active magnetic nanoparticles, according to animplementation.

FIG. 4 is an example transmission electron microscopy (TEM) image of theSERS-active magnetic nanoparticle, according to an implementation

FIG. 5A-5C illustrates detection performances of the magneticallyenhanced SERS detection, according to an implementation.

FIG. 6 illustrates detection performances using the magnetic SERSnanoparticles that are embedded with organic Raman markers, according toan implementation.

FIG. 7 is a flow diagram illustrating an example tracer detectionprocess, according to an implementation.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

This disclosure generally describes methods and systems for detectingtracers in a hydrocarbon reservoir. In some implementations, tracerstudies can be used to collect data for the subsurface fluid flowanalysis. In a tracer study, one or more tracers can be injected at aninjection site of the reservoir. The tracer can mix with the fluid inthe subsurface under the injection site. For example, the tracer candiffuse into the fluid or can mix with the fluid due to advection. Aftersome time, fluid samples can be collected at a producing site foranalysis. The propagation patterns of the tracers between the injectingsite and the producing site can be used to determine the presence andlocation of flow barriers and fractures between the two sites in thereservoir. In some cases, multiple injection sites and multipleproducing sites can be selected in a reservoir. Tracers can be injectedin each of the multiple injection sites and fluid samples can becollected at each of the multiple producing sites to analyze the fluidpattern of the entire reservoir.

In some implementations, surface-enhanced Raman scattering (SERS) can beused as a detection technique to determine whether tracers have beencollected at the producing sites. Raman spectroscopy can be used tomeasure inelastic scattering due to the interaction between incidentmonochromatic light and the induced molecular vibrations of samples. Theresults from these responses are used to determine material propertiesand the delineation of the presence of certain molecular species. TheRaman signal may provide a weak signal; thus it may be difficult todetect tracers that are low in concentration. Surface-enhanced Ramanscattering (SERS) can be used to enhance the Raman signal by an order ofmagnitude of 10⁸-10¹⁵. The SERS method enhances the Raman response whenmolecules are placed on or near a roughened metal surface or metalnanostructure such as gold, platinum, silver, copper, or the like.

In some cases, magnetic functionality can be incorporated in SERS-activenanoparticles to further enhance the detection performance. By mixingtracers and specially designed SERS-active particles in the subsurfacefluid and magnetically aggregating the SERS-active particles, thetracers are concentrated to a small area and interact with the SERShotspots, and thus the Raman signal can be enhanced and detectionperformance can be enhanced.

FIG. 1 is a schematic diagram that illustrates an example tracerdetection system 100, according to an implementation. The example tracerdetection system 100 includes a first wellbore drilling system 102,located at an injection site. The first wellbore drilling system 102 canbe implemented to inject one or more tracers 122 that can mix withsubsurface fluid 120. The example tracer detection system 100 alsoincludes a second wellbore drilling system 110 located at a producingsite. The second wellbore drilling system 110 can be implemented toextract subsurface fluid 120 at the producing site. The example tracerdetection system 100 also includes a tracer detection platform 112located at the producing site.

A wellbore drilling system, for example, the first wellbore drillingsystem 102 and the second wellbore drilling system 110, can beimplemented to inject fluids into a subsurface of a reservoir, extractfluids from the subsurface of the reservoir, or a combination thereof.For example, the first wellbore drilling system 102 can inject fluidinto the subsurface using a wellbore at an injection site. The secondwellbore drilling system 110 can extract subsurface fluid using awellbore at a producing site.

The tracer detection platform 112 is a device that perform tracerdetection of the fluids that are extracted at the producing site. In theillustrated example, the tracer detection platform 112 can be configuredto perform magnetically enhanced SERS detections.

FIG. 2 illustrates a tracer detection platform 210 before a magneticfield is applied and a tracer detection platform 220 after the magneticfield is applied, according to an implementation. In the platform 210,the subsurface fluid containing tracers 214 is extracted at theproducing site and flows through a flow channel 215. The magnetic SERSnanoparticles 212 are mixed with the fluid. Without applying a magneticfield, the magnetic SERS nanoparticles 212 are distributed randomly inthe fluid. Consequently, the metallic “hotspots” provided by themagnetic SERS nanoparticles 212 are also distributed randomly in thefluid.

In the platform 220, the subsurface fluid containing tracers 224 isextracted at the producing site and flows through a flow channel 225. Ateach detection time point, the magnetic SERS nanoparticles 222 areinjected into the flow channel 225 and mixed with the fluid. A magneticfield 226 is applied. In some implementations, the magnetic field 226can be generated using a neodymium permanent magnet, and the magneticfield 226 can be concentrated onto an attached needle tip which point tothe sample chamber The activation of the magnetic field 226 causes themagnetic SERS nanoparticles 222 to concentrate into a detection regionin the flow channel 225. Therefore, the tracers 224 interact with themetallic “hotspots” provided by the magnetic SERS nanoparticles 222 inthe detection region. An optical source 228 generates an optical signalon the detection region to excite the SERS signals. The optical source228 can be a laser device that generates a laser beam. In someimplementations, the optical signal can be visible beams, for example,having wavelengths of 488 nm, 514 nm, 532 nm or 633 nm or near infrared(NIR) wavelengths at 785 nm or 1064 nm. The SERS signals can be detectedto determine the presence of the tracers 224. At the end of detectionwindow, the flow channel 225 is flushed and the fluid, including thetracers 224 and nanoparticles 222, is released into a waste collectionstream. This process can be repeated for each measurement time point,thus providing a fresh set of SERS active particles for eachmeasurement. The material consumption for the measurements is lowbecause the amount of SERS-active particles injected for eachmeasurement can be low.

The flow channel 225 is a conduit that is used to collect and separateproduced fluids. In some cases, the flow channel 225 can be amicrofluidic system. The microfluidic system provides simple samplecollection, and magnetic force-induced nanoparticle migration. Themicrofluidic system can be a flow cell or chips with optical transparentwindow such as quartz. Once the superparamagnetic nanoparticles areinjected or mixed into the fluid with the anlaytes, the magnet can beplaced nearby the channel of the flow cell to collect nanoparticles. Asshown in FIG. 2, a well-defined amount of superparamagnetic particlescan be injected, mixed with analytes and captured in a localized area onthe channel side wall (dosing) of the flow channel 225 near the tip ofmagnet. Furthermore, the captured superparamagnetic particles on theflow channel 225 can be released into the flow of the fluid whichcontains the analytes in a controlled manner either by increasing rateof the sample flow or reducing strength of magnetic field. The strengthof magnetic field can be reduced by increasing distance betweenparticles inflow cell and the magnet. This approach provides a betterSERS signal acquisition from localized superparamagnetic nanoparticlesin the focal area.

Returning to FIG. 1, the tracer 122 can be any analytes that are used inthe hydrocarbon field for subsurface fluid flow analysis. In oneexample, the tracer 122 can be a 4-fluorobenzoic acid (FBA) analyte.Other examples of the tracer 122 include organic dyes such asfluorescein analyte and fluorescein isothiocyanate (FITC) analyte. Theanalytes can include liquid type chemicals, gas phase analytes in oilfield, or a combination thereof.

FIG. 3 is a schematic diagram that illustrates an example process 300for producing the SERS-active magnetic nanoparticles, according to animplementation. At step 310, the magnetic core particles, for example,Fe₃O₄, are incorporated into a non-magnetic particle shell, for example,SiO₂, to generate an incorporated particle 312. At step 320, theincorporated particle 312 is decorated with metallic particles, forexample Ag or Au, to create SERS hotspots on the SERS-active magneticnanoparticle 322. In some cases, the SERS-active magnetic nanoparticle320 can also be decorated with other functionalizing materials toencourage the analyte materials to interact with the hotspots andimprove SERS enhancement. In some cases, other magnetic materials can beused as the core seed particles, such as γ-Fe₂O₃, MnFe₂O₄, or CoFe₂O₄.In addition, other materials that are not Raman active can be used asshell, such as TiO₂ or ZrO₂.

Furthermore, the concentration and spacing of between the Ag particlescan be adjusted to generate hotspots for optimizing SERS signalenhancement. The magnetic components (Fe₃O₄) and hotspot generators (Ag)can be also adjusted to produce the optimal collection efficiency andSERS signal enhancement. To improve the efficiency and the detectionperformance in the flow system, the adjustment of flow rate (for examplelowering flow rate) and magnetic field (for example increasing magneticfield) during particle capture can be optimized by monitoring SERSsignals from the controlled magnetic SERS nanoparticle aggregates withanalytes.

Following is an example procedure that can be used to produce oneexample batch of SERS-active magnetic nanoparticles. First,superparamagnetic colloidal Fe₃O₄ nanoparticles are synthesized byadding FeCl₃.6H₂O (2.7 g) and FeSO₄.7H₂O (1.39 g) in 100 ml of waterwith vigorous stirring. In some cases, FeCl₂.4H₂O can be used instead ofFeCl₃.6H₂O. Next, 10 ml of NH₃.H₂O (29.5%) are added at 80° C. in awater bath for 20 minutes. After the formation of blacksuperparamagnetic nanoparticles, the particles are drawn together usingstrong magnet and redispersed in deionized water several times to rinse.The superparamagnetic nanoparticles are then coated with SiO₂(Fe₃O₄@SiO₂) by adding them to a microemulsion containing 27.5 g ofIGEPAL CO-720 in 22.0 ml of hexanol plus 170 ml of cyclohexane. Aftervigorous stirring, 1 ml of (3-Aminopropyl) triethoxysilane and 0.25 mLof tetraethyl orthosilicate (TEOS) is added and stirred for 2 hrs. Next,0.2 ml of (3-Mercaptopropyl) trimethoxysilane is added by stirring for12 hours to finalize the SiO₂ coating. Ag nanoparticles are thenattached to the Fe₃O₄@SiO₂ particles. Silver nanoparticles aresynthesized by adding 0.002 M AgNO₃ (100 ml) into 0.01 M NaBH₄ (100 ml)and stirring for 3 hours. Ag nanoparticles are added into preparedFe₃O₄@SiO₂ with volume ratios of 175:1 (Ag nanoparticle solution:Fe₃O₄@SiO₂ nanoparticles) and shaken (150 rpm) for 12 hours. FIG. 4 isan example transmission electron microscopy (TEM) image of theSERS-active magnetic nanoparticle, according to an implementation. TheseSERS-active magnetic nanoparticles can concentrate into a small regionif a magnet is placed close to the solution containing the SERS-activemagnetic nanoparticles.

FIG. 5A-5C illustrate detection performances of the magneticallyenhanced SERS detection, according to an implementation. Thesemeasurements are taken using a Raman spectrometer with an excitation of532 nm and the limit of detection (LOD) can be determined by monitoringthe characteristic peaks of the analyte molecule. Other wavelengths canbe used for other analyte materials. FIG. 5A shows the detectionperformance of a solution of fluoresce analytes mixed with SERS-activemagnetic nanoparticles. As shown in FIG. 5A, the limit of detection(LOD) can be determined at 10 μM for Fluorescein. FIG. 5B shows thedetection performance of a solution of fluorescein isothiocyanate (FITC)analytes mixed with SERS-active magnetic nanoparticles. As shown in FIG.5B, the limit of detection (LOD) can be determined at 10 nM for FITC.FIG. 5C shows the detection performance of a solution of 4-fluorobenzoicacid (FBA) analytes mixed with SERS-active magnetic nanoparticles. FBAis a material that is commonly used as tracers in oil fields. As shownin FIG. 5C, the limit of detection (LOD) can be determined at about 100μM for FBA.

The LOD for FBA can be further improved by using specially selectedparticle coatings for specific tracer detection. For example, SERSnanoparticles can be selectively coated by acrylamide usingcharge-transfer interactions or polyelectrolytes using electrostaticinteractions. This coating chemistry can be achieved by mixing ofcoating materials with SERS nanoparticles prior to the exposure toanalyte molecules. Magnetic field can then be turned on for SERSmeasurement.

In some cases, organic Raman markers can be embedded into the magneticSERS nanostructures. This approach can make the magnetic SERSnanoparticles into highly sensitive optical tracers. FIG. 6 illustratedetection performances using the magnetic SERS nanoparticles that areembedded with organic Raman markers according to an implementation. Asshown in FIG. 6, the LOD can reach to 100 ppb level using embeddedorganic Raman markers. In addition, embedding different organic dyes,for example FITC, RBITC or thionine, that have specific Raman spectrainto the magnetic SERS nanostructures can generate various barcoded oilfield tracers.

FIG. 7 is a flow diagram illustrating an example tracer detectionprocess 700, according to an implementation. The process 700 can beimplemented using additional, fewer, or different steps, which can beperformed in the order shown or in a different order. At 702, a traceris injected at a first location in a reservoir. The tracer mixes withsubsurface fluid in the reservoir. At 704, fluid samples are collectedat a second location in the reservoir. At 706, a magneticsurface-enhanced Raman scattering (SERS) particle is mixed with thefluid samples. At 708, a magnetic field is applied to the mixed fluidsamples. At 710, the fluid samples are analyzed to detect a presence ofthe tracer.

Described implementations of the subject matter can include one or morefeatures, alone or in combination.

For example, in a first implementation, a method comprises: injecting atracer at a first location in a reservoir, wherein the tracer mixes withsubsurface fluid in the reservoir; collecting fluid samples at a secondlocation in the reservoir; mixing a magnetic surface-enhanced Ramanscattering (SERS) particle with the fluid samples; applying a magneticfield to the mixed fluid samples; and analyzing the fluid samples todetect a presence of the tracer in the fluid samples.

The foregoing and other described implementations can each, optionally,include one or more of the following features:

A first feature, combinable with any of the following features, whereinthe magnetic SERS particle includes a magnetic core particle that isincorporated into a non-magnetic particle shell, the non-magneticparticle shell being decorated with metallic particles.

A second feature, combinable with any of the following features, whereinthe magnetic core particle comprises at least one of an Fe₃O₄, γ-Fe₂O₃,MnFe₂O₄, or CoFe₂O₄ particle.

A third feature, combinable with any of the following features, whereinthe metallic particles comprise at least one of an Ag or Au particle.

A fourth feature, combinable with any of the following features, whereinthe non-magnetic particle shell comprises SiO₂.

A fifth feature, combinable with any of the following features, whereinthe magnetic SERS particle is synthesized using FeCl₃.6H₂O andFeSO₄.7H₂O.

A sixth feature, combinable with any of the following features, whereinthe magnetic SERS particle is synthesized using FeCl₂.4H₂O andFeSO₄.7H₂O.

A seventh feature, combinable with any of the following features,wherein the magnetic SERS particle is synthesized using microemulsionthat contains IGEPAL CO-720 and cyclohexane.

An eighth feature, combinable with any of the following features,wherein the magnetic SERS particle is synthesized using triethoxysilaneand tetraethyl orthosilicate (TEOS).

A ninth feature, combinable with any of the following features, whereinthe magnetic SERS particle is synthesized by adding AgNO₃ into M NaBH₄.

A tenth feature, combinable with any of the following features, whereinthe magnetic SERS particle is mixed with the fluid samples in amicrofluidic system.

An eleventh feature, combinable with any of the following features,wherein the microfluidic system comprises a flow cell.

A twelfth feature, combinable with any of the following features,wherein the magnetic field is applied by placing a magnet near a channelof the flow cell.

A thirteenth feature, combinable with any of the following features,wherein the tracers are fluorobenzoic acids (FBAs) analytes.

A fourteenth feature, combinable with any of the following features,wherein the magnetic SERS particle is embedded with organic Ramanmarkers.

In a second implementation, a magnetic surface-enhanced Raman scattering(SERS) particle comprises: a non-magnetic particle shell that isdecorated with metallic particles, wherein the metallic particlescomprise at least one of an Ag or Au particle; and a magnetic coreparticle that is incorporated into the non-magnetic particle shell,wherein the magnetic core particle comprises at least one of an Fe₃O₄,γ-Fe₂O₃, MnFe₂O₄, or CoFe₂O₄ particle.

The foregoing and other described implementations can each, optionally,include one or more of the following features:

A first feature, combinable with any of the following features, whereinthe non-magnetic particle shell comprises SiO₂.

A second feature, combinable with any of the following features, whereinthe magnetic SERS particle is synthesized using microemulsion thatcontains IGEPAL CO-720 and cyclohexane.

A third feature, combinable with any of the following features, whereinthe magnetic SERS particle is synthesized using triethoxysilane andtetraethyl orthosilicate (TEOS).

A fourth feature, combinable with any of the following features, whereinthe magnetic SERS particle is synthesized by adding AgNO₃ into NaBH_(4.)

This description is presented to enable any person skilled in the art tomake and use the disclosed subject matter, and is provided in thecontext of one or more particular implementations. Various modificationsto the disclosed implementations will be readily apparent to thoseskilled in the art, and the general principles defined herein may beapplied to other implementations and applications without departing fromscope of the disclosure. Thus, the present disclosure is not intended tobe limited to the described and/or illustrated implementations, but isto be accorded the widest scope consistent with the principles andfeatures disclosed herein.

Accordingly, the previous description of example implementations doesnot define or constrain this disclosure. Other changes, substitutions,and alterations are also possible without departing from the spirit andscope of this disclosure.

What is claimed is:
 1. A method, comprising: injecting a tracer at afirst location in a reservoir, wherein the tracer mixes with subsurfacefluid in the reservoir; collecting fluid samples at a second location inthe reservoir; mixing a magnetic surface-enhanced Raman scattering(SERS) particle with the fluid samples; applying a magnetic field to themixed fluid samples; and analyzing the fluid samples to detect apresence of the tracer in the fluid samples.
 2. The method of claim 1,wherein the magnetic SERS particle includes a magnetic core particlethat is incorporated into a non-magnetic particle shell, thenon-magnetic particle shell being decorated with metallic particles. 3.The method of claim 2, wherein the magnetic core particle comprises atleast one of an Fe₃O₄, γ-Fe₂O₃, MnFe₂O₄, or CoFe₂O₄ particle.
 4. Themethod of claim 2, wherein the metallic particles comprise at least oneof an Ag or Au particle.
 5. The method of claim 2, wherein thenon-magnetic particle shell comprises SiO_(2.)
 6. The method of claim 2,wherein the magnetic SERS particle is synthesized using FeCl₃.6H₂O andFeSO₄.7H₂O.
 7. The method of claim 2, wherein the magnetic SERS particleis synthesized using FeCl₂.4H₂O and FeSO₄.7H₂O.
 8. The method of claim2, wherein the magnetic SERS particle is synthesized using microemulsionthat contains IGEPAL CO-720 and cyclohexane.
 9. The method of claim 2,wherein the magnetic SERS particle is synthesized using triethoxysilaneand tetraethyl orthosilicate (TEOS).
 10. The method of claim 2, whereinthe magnetic SERS particle is synthesized by adding AgNO₃ into M NaBH₄.11. The method of claim 2, wherein the magnetic SERS particle is mixedwith the fluid samples in a microfluidic system.
 12. The method of claim11, wherein the microfluidic system comprises a flow cell.
 13. Themethod of claim 12, wherein the magnetic field is applied by placing amagnet near a channel of the flow cell.
 14. The method of claim 1,wherein the tracer is a fluorobenzoic acids (FBAs) analyte.
 15. Themethod of claim 1, wherein the magnetic SERS particle is embedded withorganic Raman markers.
 16. A magnetic surface-enhanced Raman scattering(SERS) particle, comprising: a non-magnetic particle shell that isdecorated with metallic particles, wherein the metallic particlescomprise at least one of an Ag or Au particle; a magnetic core particlethat is incorporated into the non-magnetic particle shell, wherein themagnetic core particle comprises at least one of an Fe₃O₄, γ-Fe₂O₃,MnFe₂O₄, or CoFe₂O₄ particle; and wherein the magnetic SERS particle issynthesized using microemulsion that contains IGEPAL CO-720 andcyclohexane.
 17. The magnetic SERS particle of claim 16, wherein thenon-magnetic particle shell comprises SiO₂. 18-19. (canceled)
 20. Themagnetic SERS particle of claim 16, wherein the magnetic SERS particleis synthesized by adding AgNO₃ into NaBH_(4.)
 21. A magneticsurface-enhanced Raman scattering (SERS) particle, comprising: anon-magnetic particle shell that is decorated with metallic particles,wherein the metallic particles comprise at least one of an Ag or Auparticle; a magnetic core particle that is incorporated into thenon-magnetic particle shell, wherein the magnetic core particlecomprises at least one of an Fe₃O₄, γ-Fe₂O₃, MnFe₂O₄, or CoFe₂O₄particle; and wherein the magnetic SERS particle is synthesized usingtriethoxysilane and tetraethyl orthosilicate (TEOS).